Use APKPure App
Get Simple Interval Timer(인터벌타이머, old version APK for Android
Prosty zegar interwałowy (timer interwałowy, minutnik interwałowy, zegarek treningowy, zegarek bokserski)
It's simple and easy to use.
Frequently used exercise time can be easily used by saving it as a time set.
5 seconds before you start exercising, you can hear the sound or vibration.
Also you can use Korean and English.